Abstract

Carnivore-rich fossil sites are uncommon in the fossil record and, accordingly, provide
valuable opportunities to study predators from vantages that are rarely applied to ancient
faunas. Through stable isotopes of carbon and a Bayesian mixing model, we analyze
time-successive (nearly contemporaneous), late Miocene carnivoran populations from two
fossil sites (Batallones-1 and Batallones-3) from central Spain. Stable isotopes of carbon
in tooth enamel provide a reliable and direct methodology to track ancient diets. These
two carnivoran-dominated fossil sites display differences in the composition and abundance
of the carnivoran species, with some species present at both sites and some present only
at one site. This disparity has been interpreted as the consequence of habitat differences
between Batallones-1, the older site, and Batallones-3, the younger site. However, carbon
isotope values of carnivore and herbivore tooth enamel suggest a common habitat of
C3 woodland originally present at both sites. The differences in the carnivoran
faunas rather may be the consequence of the dynamics of species entrance and exit from the
Madrid Basin during the time elapsed between Batallones-1 and Batallones-3 and changes in
population densities due to biotic factors. We infer higher levels of interspecific
competition in Batallones-3 than in Batallones-1 because of the larger number of
similar-sized, sympatric predators; the clear overlap in their δ13C values
(except for the amphicyonid Magericyon anceps); and similarity of their
preferred prey: the hipparionine horses. Finally, carbon stable isotopic composition of
Indarctos arctoides teeth implies that this ursid was a carnivorous
omnivore rather than a herbivorous omnivore. This work demonstrates the insights that
stable isotopes can provide in characterizing the feeding ecology and trophic interactions
of ancient carnivoran taxa.